Technical Abstract:
Soy is a major plant source of dietary protein to humans. Epidemiologic studies show that soy consumption may be associated with a reduction in cancer risk in humans. The purpose of this study was to conduct a meta-analysis on the association between soy and prostate cancer in men. We systematically reviewed studies obtained through a thorough MEDLINE literature search and identified 15 studies on soy consumption and eight on isoflavone intake in relation to prostate cancer risk. We conducted this analysis using a random-effects model in which studies with smaller standard error of estimate are given greater weight in the summary measure. Our analysis of studies on soy intake yielded an overall risk estimate of 0.74 (95% confidence interval: 0.63, 0.89; P = 0.001). When separately analyzed, studies on non-fermented soy foods yielded an overall risk estimate of 0.70 (0.56, 0.88; P = 0.002) and those on fermented ones yielded 1.02 (0.73, 1.42; P = 0.922). The analysis of studies on isoflavones yielded an overall risk estimate of 0.88 (0.76, 1.02; P = 0.085). When analyzed on the basis of daily isoflavone intakes, we found an overall risk estimate of 0.63 (0.41, 0.96; P = 0.03) from studies at mg/day and 0.99 (0.85, 1.16; P = 0.909) from those at µg/day, respectively. Results of this analysis suggest that consumption of soy foods is associated with a reduction in prostate cancer risk in men.